1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a fax machine, a printer or the like. More particularly, the present invention relates to a charging device comprising a discharge wire for charging an image carrier such as a photoconductive member or the like, and a cleaning member for cleaning the discharge wire, and to a process cartridge comprising the charging device.
2. Description of the Related Art
Known such image forming apparatuses include image forming apparatuses comprising a charging device, for instance of scorotron type, having a discharge wire for charging an image carrier such as a photoconductive member or the like. With the passage of time, contamination accumulates on the discharge wire, impairing thereby the discharge performance of the discharge wire.
To prevent loss of discharge performance, these charging devices comprise a cleaning member for wiping clean the surface of the discharge wire, as described in, for instance, Japanese Patent Application Laid-open No. 2004-317702, Japanese Patent Application Laid-open No. H10-301368, Japanese Patent No. 3619057, Japanese Patent Application Laid-open No. H08-095349, and Japanese Patent Application Laid-open No. 2003-050496.
Known cleaning members include cleaning members comprising an abrasive for increasing the removability of contamination adhered to the surface of the discharge wire, for instance as disclosed in Japanese Patent Application Laid-open No. 2004-317702, Japanese Patent Application Laid-open No. H10-301368, Japanese Patent No. 3619057, and Japanese Patent Application Laid-open No. H08-095349. Other known cleaning members do not comprise an abrasive, for instance as disclosed in Japanese Patent Application Laid-open No. 2003-050496, on the grounds that the abrasive comprised in the cleaning member may whittle away the discharge wire.
A protective film such as an oxide film, gold plating or the like, may also be formed on the surface of the discharge wire, as disclosed in, for instance, Japanese Patent Application Laid-open No. H08-095349, and Japanese Patent Application Laid-open No. 2003-050496.
Protection of the discharge wire is high when using an oxide film, having high wear resistance, as the protective film, even when the cleaning member comprises an abrasive. However, contamination adheres readily onto oxide films, and hence the discharge wire must be cleaned frequently. Image formation cannot take place during wire cleaning, and hence highly frequent cleaning is problematic in that it adds to image forming apparatus downtime.
By contrast, using gold plating as the protective film is advantageous in that contamination adheres less readily to the protective film. However, the gold-plating protective film is readily damaged when the cleaning member comprises an abrasive, as described in Japanese Patent Application Laid-open No. 2003-050496.
In terms of downtime of the image forming apparatus, however, it is preferable to gold-plate the discharge wire, to hinder adhesion of contamination onto the surface of the discharge wire. At the same time, a cleaning member comprising an abrasive is also preferable, in terms of cleanability of the discharge wire. Moreover, the gold plating must also be preserved in good condition as time goes by.